This invention relates to a liquid epoxy resin composition which cures into a cured product having improved adhesion to the surface of silicon chips and especially photosensitive polyimide resins and nitride films, and a semiconductor device which is sealed with the cured product of the liquid epoxy resin composition.
The trend toward smaller sizes, lighter weights and increased capabilities in electrical equipment has led to a shift in the dominant semiconductor mounting process from pin insertion to surface mounting. Progress of semiconductor devices toward a higher degree of integration entails the enlargement of dies having a size as large as 10 mm or more per side. For semiconductor devices using such large size dies, attention is paid to the problems that greater stresses are applied to the die and the sealant during solder reflow, separation occurs at the interface between the sealant and the die or substrate, and the package cracks upon substrate mounting.
Prior art liquid epoxy resin compositions are less adherent to the surface of silicon chips and especially photosensitive polyimide resins and nitride films. In the semiconductor art, there remains a need for improving adhesion to such materials.
An object of the invention is to provide a liquid epoxy resin composition which cures into a cured product having improved adhesion to the surface of silicon chips and especially photosensitive polyimide resins and nitride films. Another object of the invention is to provide a semiconductor device which is sealed with the cured product of the liquid epoxy resin composition.
The invention addresses a liquid epoxy resin composition comprising a liquid epoxy resin, a curing accelerator, an inorganic filler, and optionally, a curing agent. It has been found that when an indene polymer in the form of a copolymer of indene and styrene and/or a ternary copolymer of indene, chroman and styrene, having a number average molecular weight of 200 to 2,000, is blended in the composition in an amount of 0.1 to 20 parts by weight per 100 parts by weight of the liquid epoxy resin, by previously melt mixing the indene polymer with a part or all of the liquid epoxy resin and then compounding the melt premix with the remaining components, the resulting liquid epoxy resin composition is effectively adherent to the surface of silicon chips and especially photosensitive polyimide resins and nitride films and thus suitable as a sealant for large die size semiconductor devices. Although indene polymers are known as a semiconductor encapsulant to be molded, they have not been used as a component of a liquid epoxy resin composition sealant because they are solid at room temperature. By limiting the amount of the indene polymer and melt premixing it with a liquid epoxy resin, there can be obtained an epoxy resin composition which is liquid at room temperature and which is effectively adherent to the surface of silicon chips and especially photosensitive polyimide resins and nitride films and thus suitable as a sealant for large die size semiconductor devices. The invention is predicated on this finding.
The invention provides a liquid epoxy resin composition comprising (A) a liquid epoxy resin, (B) an optional curing agent, (C) a curing accelerator, (D) an inorganic filler, and (E) an indene polymer. The indene polymer (E) is a copolymer of indene and styrene and/or a ternary copolymer of indene, cumarone, and styrene, having a number average molecular weight of 200 to 2,000, and is present in an amount of 0.1 to 20 parts by weight per 100 parts by weight of component (A) or components (A) and (B) combined. The indene polymer (E) is previously melt mixed with a part of all of the liquid epoxy resin (A) prior to compounding with the remaining components. Also contemplated herein is a semiconductor device which is sealed with the cured product of the liquid epoxy resin composition.